Programmable power supplies which are known in the art typically use a keyboard control through an IEEE 488 bus. By using a programmable power supply, the voltage and current parameters may be controlled by an operator, instead of requiring the use of a number of different power supplies to obtain various voltages and currents. Typically, programmable power supplies comprise linear power supplies in which, in order to control the output voltage, a negative feedback loop is used to vary the conduction of the active element. The linear power supply has the advantage that it is relatively efficient and provides a very clean output. However, the linear power supply has the disadvantage that it requires a line transformer to reduce the line voltage significantly and the linear power supply is relatively inefficient and heavy compared to a switching power supply, although the linear power supply provides a cleaner performance.
A switching power supply generally is significantly smaller than a linear power supply and typically uses relatively high frequency pulses so that lightweight magnetics may be used. However, the switching power supply does not provide an output that is as clean as the linear power supply and thus, where a clean output is required, a linear power supply is typically used although it is less efficient, more expensive and heavier.
It is an object of the present invention to combine the advantages of a switching power supply with the advantages of the linear power supply, in a programmable system.
Other objects and advantages of the present invention will become apparent as the description proceeds.